Spaceflight Insider

Spitzer Space Telescope confirms super-Earth nearby

With exoplanets found as far away as 13,000 light years, it appeared that worlds like our own were not in “the neighborhood”. Using NASA’s Spitzer Space Telescope, scientist have confirmed the existence of a rocky planet somewhat similar in size to Earth – and it is just 21 light-years away. 

The initial discovery of the exoplanet, designated HD219134bwas made by the High Accuracy Radial velocity Planet Searcher (HARPS-North) instrument on the Italian 3.6 meter Galileo National Telescope. This telescope is located in the Canary islands off the coast of Morocco. The reflecting telescope is one of the largest operated by the Roque de Los Muchachos Observatory.

In addition to HD219134b, the HARPS-North instrument also found three more planets in the same system. However, these other worlds were located further out from their parent star.

Spitzer Space Telescope in the clean room photo credit Carleton Bailie SpaceFlight Insider

The Spitzer Space Telescope. Photo Credit: Carleton Bailie / SpaceFlight Insider

“Most of the known planets are hundreds of light-years away. This one is practically a next-door neighbor,” said astronomer Lars A. Buchhave of the Harvard-Smithsonian Center for Astrophysics. Buchhave along with Michael Gillon of the University of Liege in Belgium are the authors of the study on HD219134b.

This exoplanet was found using what is known as the ‘transit’ method. The technique looks for the dimming of a star as a planet or other body passes between the observer and the star. By watching for subtle shifts in the light, it is possible to determine the orbit of any planets in the star system.

This technique generally requires planets that transit their stars rather rapidly. In this case, HD219134b orbits its parent star every three days. Using a technique know as radial velocity (the gravity pull of the planet on its parent star), the planet’s mass was determined to be 4.5 times that of Earth.

The Spitzer telescope followed up on these initial observations. The telescope measured the planet using its infrared sensors to help determine the planet’s size.

Spitzer data suggests the planet is about 1.6 times the size of the Earth. With the mass and size known, the density of the planet was then calculated. The result was 3.5 ounces per cubic inch (six grams per cubic centimeter). That density puts HD219134b firmly in the rocky planet category of the so-called super-Earths.

The Spitzer telescope mission is managed for NASA’s Science Mission Directorate by the Jet Propulsion Laboratory (JPL) in Pasadena, California.

Working from an Earth-trailing orbit, some 353 miles (570 km) above our world, Spitzer is an infrared observatory and a part of NASA’s Great Observatories program.

Launched in 2003 with a planned 2.5 to 5 year mission life, Spitzer has provided large amounts of data to scientists at JPL. With its supply of liquid helium long since exhausted, Spitzer continues operating under the Warm Mission program using two remaining onboard instruments. This mission looks to study exoplanets as well as their environments.

While the planet is close in both size and mass to Earth, the similarities end there. HD219134b orbits its parent star a little too close to support life as we know it. The planet is too small to be seen, but its parent star is visible to the naked eye in the Northern Hemisphere. It resides near Polaris (the North star) close to the constellation of Cassiopeia.

Michael Gillon summed up this latest discovery as such, “Now we have a local specimen to study in greater detail. It can be considered a kind of Rosetta Stone for the study of super-Earths.”

Given the relatively close proximity to Earth, additional telescopes will now be programmed to look at HD219134b to see what additional details can be revealed about this distant world.

NASA image of exoplanet transiting in front of its parent star image credit NASA posted on SpaceFlight Insider

Exoplanets are being discovered with increasing frequency throughout the Milky Way with many scientists predicting that the discovery of an Earth-like planet will likely be made in the not-too-distant future. Image Credit: NASA



Joe Latrell is a life-long avid space enthusiast having created his own rocket company in Roswell, NM in addition to other consumer space endeavors. He continues to design, build and launch his own rockets and has a passion to see the next generation excited about the opportunities of space exploration. Joe lends his experiences from the corporate and small business arenas to organizations such as Teachers In Space, Inc. He is also actively engaged in his church investing his many skills to assist this and other non-profit endeavors.

Reader Comments

More great work from the fine folks at JPL!

Another excellent example of what can be done with a spacecraft like Spitzer which can remain useful even after its primary mission has been completed. While HD 219134b is certainly the closest confirmed rocky transiting exoplanet, there is an unconfirmed one that is even closer. While searching for transits to confirm the existence of Alpha Centauri Bb using the Hubble Space Telescope, an international team of astronomers recently announced finding a single transit-like signature suggesting another closely orbiting Earth-size planet instead.

Although the observation needs to be independently confirmed, at a distance of 4.3 light years and with a size comparable to Earth (virtually guaranteeing it is a rocky planet and not a mini-Neptune) this could end up being the closest rocky transiting exoplanet.

While not impossible for a planet to orbit a star in 3 days the likelihood that ALL of the planets “discovered” by the transit method have this fast orbit is very unlikely. Furthermore most of the planets supposedly found are ginormous, larger than any of our inner planets in our solar system & sometimes 8x or more larger than jupiter! Until they have visual evidence of the planets in other solar systems I am not convinced of the transit methodology…it’s just as likely the dimming of a star ever so slightly is just the star itself pulsing or some other interference between us & the star being monitored. So far the best method I have seen to show potential planets is where they block out the star visually (or infrared, xrays, etc) and see evidence of a planet without the “glare” of the parent star. Rudimentary but better than this method

1. Not all planets found via the transit method are “ginormous”. Kepler 37b is Mars-sized. There are plenty of others that are Earth or Neptune-sized.

2. I could understand your skepticism if the planets observed by Kepler (which uses the transit method) weren’t observed with multiple transits (showing a regular period of revolution that a dimming or pulsing would not) and if most of these planets were not also confirmed by the radial velocity method (a dimming or pulsing would not show up at in radial velocity).

As it is, I’m not sure I can understand your hesitation to accept these results. Both methods are going to be prone to a bias that will show hot Jupiter-type planets long before smaller and more distant planets show up in the data. The many hot Jupiters reported are at least partly due to this bias and not due entirely to the distribution of planets in the galactic plane.

As Joe rightly points out, not all of the planets found by the transit method are “ginormous”. The apparent disproportionate number of giant planet discoveries is because larger planets are easier to detect than smaller planets. For example, a Jupiter-sized world produces a transit signature that is ~120 times larger than an Earth-size planet. Also, planets in smaller orbits have a higher probability of having its orbit oriented by chance to produce an observable transit than a planet in a larger orbit. For example, a planet in a 3-day orbit is ~25 time more likely to produce an observable transit than a planet in a 365-day orbit. When these selection biases are taken into account, there are fewer Jupiter-size planets than Neptune-size planets which are in turn less numerous than Earth-size planets. And while there is a bunching of planets with very short orbital periods (which tells us about how some planets migrate early in their lives), there are planets being found with a large range of orbital periods out to the maximum Kepler can detect (i.e. a bit more than a year).

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